Are There Any Products or Procedures That Can Whiten Crowns?

There are no whitening products that can whiten crowns.  If you have a crown and get your teeth whitened you would need to replace your current crown.

One of the benefits to modern dentistry is color stability. Smile makeovers, where a new color is chosen, satisfy for a long time since the colors don't degrade over time. This same "benefit" can be a problem in some situations.
If a single crown was placed and later the teeth were whitened, the crown that matched will no longer blend in. Same with fillings. Before teeth are whitened, people should be informed that dental restorations would need to be replaced/upgraded.
If you have a crown that is not the color that you would like it to be, it must be replaced.

The best way to whiten a crown is to replace the crown with a crown made in a lighter shade.  This is why it can be helpful to ask yourself if you like the color of your teeth before getting a crown done.  If you'd like to have whiter teeth, it's usually better to whiten them and then get any restorative work done.  Then when you go to shade match for your crown, for example, it will be more accurately matched to the lighter color of your whitened teeth.  

Hi:If your crowns are stained due to drinking tea, coffee or smoking, then Oral Essentials Whitening strips can help.  However, if you don’t like the color of your crowns, then they have to be replaced with a new one.Best,Dr. Maddahi

Kitty, thank you for your great question. The best procedure I know of to whiten crowns is to change them. In case crowns were done recently and there is nothing wrong with them except esthetically, a second option is to place Lumineers/veners over them. That's ok in some caes.